Tyre bead wire and process for production thereof

ABSTRACT

A tire bead wire and a process for producing a tire bead where a carbon steel wire rod containing carbon in a range of 0.61% or more to 0.65% or less in weight percent and having a diameter in a range of 5.5 mm to 6.5 mm is wiredrawn through a single wiredrawing process to a predetermined final wiredrawing diameter having a true strain in a range of 2.0 to 4.0 and is turned to a pearlite structure in which ferrite and cementite are drawn in parallel with a narrow interval therebetween.

TECHNOLOGICAL FIELD

The present invention relates to a tyre bead wire and a production process therefor used in producing bead cores made of carbon steel wires being reinforcements of automotive tyres.

BACKGROUND ART

Tyre bead wires are required to be tough and high in durability. In general, as the tyre bead wires, there have been used those which are 1.55 mm in diameter and equal to 1880 N/mm² or higher in tensile strength or those which are 0.94 mm in diameter and equal to 1840 N/mm² or higher in tensile strength. Like this, the bead wires require a high tensile strength. Thus, as material wires of hard steel wires, there has been used a high-carbon steel wire rod which is primarily 5.5 mm in diameter and has a carbon content in a range of 0.69-0.86 weight percents, and the bead wire rod is manufactured by being subjected to a wiredrawing process in which a total area-reduction rate is in a range of 92-97 percents or so.

The high-carbon steel wire rod is regulatively cooled after being hot-rolled if need be, and the resultant wire rod of pearlite structures having a diameter in a range of 5.5-6.5 mm is repetitively subjected to wiredrawing processes and patenting treatments to become a diameter in a range of 3.0-2.0 mm for a final wiredrawing. The wire rod of this diameter, after being subjected to the final wiredrawing, is then subjected to a bluing treatment and a plating treatment and is coiled, whereby there can be manufactured a steel cord that is usable as reinforcement in radial tyres, conveyor belts or the like. For example, Patent Document 1 describes a process for producing steel cords of this kind.

Further, for example, Patent Document 2 describes a process for performing a second wiredrawing process without performing an intermediate patenting treatment. In the process described in Patent Document 2, by exerting a mechanical external force on a steel material to deform the same, the temperature of the steel material is raised to sufficiently dry borax in the second wiredrawing process, so that the second wiredrawing process can be realized without suffering seizure and wire breaking.

PRIOR ART DOCUMENTS

-   Patent Document 1: JP7-3338 A -   Patent Document 2: JP2008-284581 A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In order to manufacture a wire of a predetermined diameter through a first wiredrawing process only (omission of the second wiredrawing process) by omitting the intermediate patenting treatment, it is necessary to use a material wire rod of a special diameter which is thinner than 5.5 mm for general purpose in terms of preventing wire breaking due to a high-stress processing as well as of maintaining the post-wiredrawing strength at a predetermined strength. However, unlike the case of using a wire rod of 5.5 mm diameter for general purpose, the wire rod of the special wire diameter (e.g., 5.0 mm or less in diameter) which is small in production volume is required to be repetitively subjected to wiredrawing processes and patenting treatments, and this gives rise to problems that increase the cost for the material wire rod and thus, the production cost for bead wires and hence, for tyres.

Further, in recent years, in an aspect of environment, tyres are increased in a rate to be used twice with treads repaired after a first long-term use, and thus, requirements for adhesive strength and durability after the long-term use have been increasing in a respect of adhesion of bead wires to surrounding rubber.

Further, in an aspect of production, it is conventional that for a continuous production, a material wire rod as material is subjected to a wiredrawing process as a wire rod in use is welded to a wire rod to be used next. However, with an increase in carbon content, such welding causes a remarkable change in structure at a portion that was heated at a high temperature, and this gives rise to a problem that a large influence is given on strength and toughness.

The present invention has been made in order to solve the foregoing problems in the prior art, and an object thereof is to provide a tyre bead wire and a production process for the same which are capable of employing a carbon steel wire rod having a general-purpose wire diameter whose carbon content in weight percent is in a range of 0.61% or more to 0.65% or less, and of wiredrawing the rod to a predetermined final wiredrawing diameter suitable for bead wires through one process without performing a patenting treatment.

Measures for Solving the Problem

The feature of the invention in a tyre bead wire according to Claim 1 resides in that a carbon steel wire rod containing carbon in a range of 0.61% or more to 0.65% or less in weight percent and having a diameter in a range of 5.5 mm to 6.5 mm is wiredrawn through one wiredrawing process to a predetermined final wiredrawing diameter with a true strain in a range of 2.0 to 4.0 and is turned to pearlite structures in which ferrite and cementite are drawn in parallel with an interval therebetween made to be narrow.

The feature of the invention in the tyre bead wire according to Claim 2 resides in that in Claim 1, the one wiredrawing process results in wiredrawing to a diameter in a range of 0.94 mm to 1.30 mm.

The feature of the invention in a tyre bead wire production process according to Claim 3 resides in that a carbon steel wire rod containing carbon in a range of 0.61% or more to 0.65% or less in weight percent and having a diameter in a range of 5.5 mm to 6.5 mm is wiredrawn through one process to a predetermined final wiredrawing diameter with a true strain in a range of 2.0 to 4.0 and that the wire rod after the wiredrawing is blued and then, is plated.

The feature of the invention in the tyre bead wire production process according to Claim 4 resides in that in Claim 3, the carbon steel wire rod being 5.5 mm in diameter is wiredrawn to a final wiredrawing diameter in a range of 0.94 to 1.30 mm.

The feature of the invention in the tyre bead wire production process according to Claim 5 resides in that in Claim 3, the carbon steel wire rod being 6.5 mm in diameter is wiredrawn to a final wiredrawing diameter in a range of 1.5 to 2.20 mm.

Effects of the Invention

In the invention of the tyre bead wire according to Claim 1, the carbon steel wire rod containing carbon in the range of 0.61% or more to 0.65% or less in weight percent and having the diameter in the range of 5.5 mm to 6.5 mm is wiredrawn through one wiredrawing process to the predetermined final wiredrawing diameter with the true strain in the range of 2.0 to 4.0 and is turned to the pearlite structures in which ferrite and cementite are drawn in parallel with the interval therebetween made to be narrow. Therefore, although the carbon steel wire rod of a general-purpose diameter is employed, it can be realized to obtain a useful tyre bead wire which is superior in tensile strength, is excellent in adhesion of the bead wire to surrounding rubber, and does not bring about the breaking of wire during the wiredrawing and the breaking of wire at welded parts thereof.

In the invention of the tyre bead wire according to Claim 2, since the one wiredrawing process results in wiredrawing to the diameter in the range of 0.94 mm to 1.30 mm, it can be realized to obtain the bead core of the diameter suitable for production of bead cores easily and efficiently.

In the invention of the tyre bead wire production process according to Claim 3, the carbon steel wire rod containing carbon in the range of 0.61% or more to 0.65% or less in weight percent and having the diameter in the range of 5.5 mm to 6.5 mm is wiredrawn through one process to the predetermined final wiredrawing diameter with the true strain in the range of 2.0 to 4.0. Therefore, it becomes possible to wiredraw the carbon steel wire rod of the relatively low carbon content at the high area-reduction rate without a patenting treatment and to wiredraw the carbon wire rod of the general-purpose wire diameter (5.5-6.5 mm diameter) through the one process to the final wiredrawing diameter suitable for bead wire without bringing about the breaking of the wire but with a required tensile strength secured.

In addition, because the carbon wire rod is low in carbon content to be softened, the workability in wiredrawing the carbon steel wire rod can be improved, and the productivity can be enhanced. Further, in continuously wiredrawing the wire rod, it becomes easier to perform a welding at the time of welding material wires which welding is required in a continuous production by using a material wire in use and another material wire to be used next, and the breaking of wire at the welded portion is made to be hard to occur.

In the invention of the tyre bead wire production process according to Claim 4, since the carbon steel wire rod being 5.5 mm in diameter is wiredrawn to the final wiredrawing diameter in the range of 0.94 to 1.30 mm, it is possible to employ the carbon steel wire rod of 5.5 mm diameter for general purpose, and an equipment for the patenting treatment can be made to be unnecessary, so that the bead wire can be manufactured at a low cost.

In the invention of the tyre bead wire production process according to Claim 5, since the carbon steel wire rod being 6.5 mm in diameter is wiredrawn to the final wiredrawing diameter in the range of 1.5 to 2.20 mm, it is possible to employ the carbon steel wire rod of 6.5 mm diameter for general purpose, and an equipment for the patenting treatment can be made to be unnecessary, so that the bead wire can be manufactured at a low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] is a view illustrating the layers of ferrite and cementite having been drawn in parallel by wiredrawing.

[FIG. 2] is a chart of an embodiment showing production processes in a tyre bead wire production process of the present invention.

[FIG. 3] is photos of the surfaces of bead wires in the state that plated surface layers are removed from the bead wires which are manufactured as shown in FIG. 2.

FORM FOR IMPLEMENTING THE INVENTION

Hereinafter, description will be made regarding a tyre bead wire production process in an implementation form of the present invention.

Bead wires for vehicle tyres are required to be tough and high in durability. The strength of a bead wire can be intensified by wiredrawing and thinning in wire diameter a wire rod which has fine pearlite structures (2-phase structure of ferrite (Fe) and cementite (Fe₃C)) and which has been subjected to a patenting treatment. Tyres which employ bead cores produced by using the bead wire made of such a wire rod can contribute to requirements for high strength, high toughness and light weight. This is because, as shown in FIG. 1, the wiredrawing process causes the crystals of high strength cementite (Fe₃C) and ferrite (Fe) to be drawn and to be oriented in parallel in the wiredrawing direction, so that the width of ferrite phases is narrowed to increase the strength. And, the thinner the wiredrawing process makes the wire diameter, the higher the strength becomes.

However, the thinner the wire diameter is made, the harder the wire rod becomes, and the flexibility is lost. Thus, the wire diameter to which the wire rod can be fined by one wiredrawing process is restrained as a matter of course. For this reason, in order to attain a desired wire diameter, it is required to carry out, after a wiredrawing process to a predetermined wire diameter, a patenting treatment to return the wire rod again to fine pearlite structures suitable for wiredrawing, and then to carry out another wiredrawing process again. By the repetition of these processes, for instance, the wire rod of 5.5 mm in wire diameter is wiredrawn to 1.20 mm diameter, and then, a bluing treatment is carried out at a temperature in a range of 380 to 480° C. to give a stretch necessary for steel wire. And, a plating treatment is carried out to enhance the adhesibility of the bead wire to surrounding rubber, and then, the bead wire is coiled by a coiler in the form of a coil. However, the process like that is required to install an equipment for the patenting treatment in the production facility.

A small-diameter material wire of, for example, 4.0 mm or 4.5 mm in wire diameter can be used in order to make the equipment for the patenting treatment unnecessary and in order to wiredraw a wire rod through one wiredrawing process to a desired wire diameter (2.20-0.94 in diameter) suitable for bead wire. However, in order to realize this, material wires of the special diameter must be obtained from steel manufacturers.

Therefore, in the present implementation form, as the material wire for bead wire, a wire rod being a carbon steel whose carbon content is in a range of 0.61-0.65 in weight percent and is lower than the carbon content of the prior at wire rod, and having a wire diameter in a range of 5.5-6.5 mm is wiredrawn through one process to a predetermined final wiredrawing diameter (2.20-0.94 mm diameter) suitable for bead wire without being subjected to a patenting treatment. Although the area reduction rate becomes larger in comparison with the area reduction rate in the prior art, the wire rod is lower in carbon content than that in the prior art and is a softer material than that in the prior art. Therefore, wiredrawing at a high area-reduction rate can be done. Moreover, as a result of wiredrawing the carbon steel of the low carbon content at the high area-reduction rate, there can be obtained a bead wire that is turned to pearlite structures in which, as shown in FIG. 1, ferrite (Fe) and cementite (Fe₃C) are narrowed in the interval therebetween and are drawn in parallel with fine and smooth structures, that can secure a tensile strength and a toughness required for bead wire, that is excellent in the adhesion to surrounding rubber, and that can prevent the breaking of wire during the wiredrawing and the breaking of wire at welded portions.

FIG. 2 shows a production process for bead wire. A carbon steel (wire rod) having a wire diameter in a range of 5.5-6.5 mm and a carbon content in a range of 0.61-0.65 in weight percent is uncoiled from a coiler (10) and has an oxide film on the surface removed by a descaling device (11). Then, the carbon steel is made to pass through a coating liquid adhesion device to adhere a coating liquid on the surface of the wire rod (12) and is dried. Thereafter, the wire rod is wiredrawn by serially arranged dry wiredrawing devices 30 through one process to a predetermined final wiredrawing diameter (2.20-0.94 mm diameter) with a true strain in a range of 2.0-4.0 (13) and is coiled by a coiler (14).

At this time, in the case of the wire diameter being 5.5 mm, the final wiredrawing diameter which is to be obtained by the wiredrawing through one process is preferably in a range of 0.94-1.30 mm diameter or so, and in the case of the wire diameter being 6.5 mm, the final wiredrawing diameter which is to be obtained by the wiredrawing through one process is preferably in a range of 1.5-2.20 mm diameter or so.

Subsequently, the wire rod which has been wiredrawn to the final wiredrawing diameter is uncoiled from the coiler (20) and then, is subjected to a bluing treatment by a bluing treatment device (21). And, the wire rod is plated by a plating treatment device (22) and is coiled by a coiler (23), whereby a tyre bead wire is produced.

In continuously producing wire rods, in order to perform the continuous production by using a material in use and a material to be used next without discontinuing the production, it is required to join the terminal end of the material in use and the starting end of the material to be used next by welding. The productivity is largely influenced in dependence on an occurrence rate of wire breakings at welded portions where a tensile load and a bending are weaker than other portions. However, welding causes each welded portion and portions close thereto having been exposed to a high temperature to be remarkably changed in structure as the carbon content in the material increases, and requires carrying out tempering. Nevertheless, the influence goes to remain and provides a large influence on tensile strength and toughness. On the other hand, in the case that the carbon content in the material is low, the occurrence rate of wire breakings caused by welding decreases, and the productivity increases.

Further, the adhesion force between a bead wire and rubber is determined in dependence on a chemical bonding force brought about by a chemical reaction between the rubber and the plated layer on the surface of the bead wire and a physical bonding force of an anchor effect to wrinkles (unevenness) on the surface of the bead wire. Therefore, although being limitative, the anchor effect, when increased, makes it possible to go up the adhesion force. Particularly, the physical bonding force by the anchor effect is effective where a tyre is subjected to a high temperature, a high moisture and repetitive strains due to a hard travelling which causes the adhesive interface between the rubber and the surface of the bead wire to deteriorate and raises the rate at which the boundary surface is exposed.

Embodiment

Next, the construction and operation effects of the present invention will be described in detail based on an embodiment.

Embodiment 1

As shown in Table 1, a hard steel wire rod of 5.5 mm in wire diameter prescribed by JIS (Japanese Industrial Standards) G3506 SWRH62A was used as a material wire rod. The chemical components were C: 0.63%, Si: 0.21% and Mn: 0.52%, and the remainder thereof was Fe and inevitable impurities. An oxide film on the surface of the material rod was removed by a descaling device, and then, the material rod was made to pass through a coating liquid adhesion device, whereby a coating liquid was adhered to the surface of the wire rod and was dried. Thereafter, by dry wiredrawing devices arranged in series, the wire rod was reduced in area through one wiredrawing process to a predetermined wire diameter being 1.20 mm diameter with a true strain in a range of 2.0-4.0. The drawn wire rod was coiled by a coiler in the form of a coil, and the coiled wire rod was uncoiled to be subjected to a bluing by being made to pass through a bath held at a temperature of 430° C. and then, to a plating treatment, whereby a bead wire was produced.

COMPARED EXAMPLE 1

As shown in Table 1, a hard steel wire rod of 5.5 mm in wire diameter prescribed by JIS G3506 SWRH72A was used as a material wire rod. The chemical components were C: 0.71%, Si: 0.22% and Mn: 0.49%, and the remainder thereof was Fe and inevitable impurities. An oxide film on the surface of the material rod were removed by the descaling device, and then, the material rod was made to pass through the coating liquid adhesion device, whereby the coating liquid was adhered to the surface of the wire rod. Thereafter, by the dry wiredrawing devices arranged in series, the wire rod was reduced in area through one wiredrawing process to the predetermined wire diameter being 1.20 mm diameter. The drawn wire rod was coiled by the coiler in the form of a coil, and the coiled wire rod was uncoiled to be subjected to the bluing by being made to pass through the bath held at the temperature of 430° C. and then, to the plating treatment, whereby a bead wire was produced.

COMPARED EXAMPLE 2

As shown in Table 1, a hard steel wire rod of 4.5 mm in wire diameter prescribed by JIS G3506 SWRH72A was used as a material wire rod. The chemical components were C: 0.72%, Si: 0.21% and Mn: 0.51%, and the remainder thereof was Fe and inevitable impurities. An oxide film on the surface of the material rod was removed by the descaling device, and then, the material rod was made to pass through the coating liquid adhesion device, whereby the coating liquid was adhered to the surface of the wire rod. Thereafter, by the dry wiredrawing devices arranged in series, the wire rod was reduced in area through one wiredrawing process to the predetermined wire diameter being 1.20 mm diameter. The drawn wire rod was coiled by the coiler in the form of a coil, and the coiled wire rod was uncoiled to be subjected to the bluing by being made to pass through the bath held at the temperature of 430° C. and then, to the plating treatment, whereby a bead wire was produced.

TABLE 1 Mechanical Properties Chemical Number of Adhesion Force (N) - Rubber Adhesion Rate (%) Kind of Steel Components Tensile Breaking Breakings Initial Waterproof (Diameter of (Weight %) Strength at Wire- at Welded Adhesion Adhesion Material Wire) C Si Mn (N/mm²) drawing Portions Property Property 1 Embodiment 1 0.63 0.21 0.52 2000 Nil 0 1320 - 95 1180 - 80 (5.5 mm) 2 Compared 0.71 0.22 0.49 2200 Many 2 1310 - 95 1135 - 80 Example 1 (5.5 mm) 3 Compared 0.72 0.21 0.51 1950 Nil 1 1275 - 90 1010 - 40 Example 2 (4.5 mm)

Tensile tests were carried out on the bead wires produced in the aforementioned embodiment 1 and compared examples 1 and 2 to test the tensile strengths (N/mm²), the situations of wire-breaking at the time of wiredrawing, and the states of wire-breaking at welded portions. The results are as described in the aforementioned Table 1.

As clear from Table 1, according to the production process in compared example 1, the wire rod with a sufficient tensile strength (2200 N/mm²) was able to be obtained, but the wire rod could not be drawn smoothly as a result that the high carbon steel of the wire diameter 5.5 mm having a large carbon content was reduced in surface to the 1.2 mm wire diameter through one process being a heavy process. As a consequence, the breaking of the wire took place at many portions thereon during the wiredrawing. Further, because of being high in carbon content, the wire rod had considerable changes in structure at the portions which were heated at a high temperature during the welding, whereby the breaking of the wire also took place at many welded portions.

Further, according to the production process in compared example 2, since the area reduction rate (the quantity in process) in the wiredrawing was smaller than that in compared example 1, the breaking of wire did not occur during the wiredrawing. The tensile strength was 1950 N/mm² in a level that did not raise any problem. However, because of being high in carbon content, as is the case of compared example 1, the wire rod had considerable changes in structure at the portions which were heated at the high temperature during the welding, whereby the breaking of the wire took place at a welded portion.

Furthermore, the carbon steel wire rod of the special wire diameter (4.5 mm) is required, and in order to obtain the carbon steel wire rod of the 4.5 mm wire diameter by the bead wire manufacture itself, an equipment is required that carries out a patenting treatment on a carbon steel wire rod for general purpose (5.5-6.5 mm diameter) purchased from a steel manufacturer. Where the bead wire manufacturer does not have the equipment, there is a constraint that the manufacturer has to obtain expensive material wires from a steel manufacturer.

On the contrary, in the aforementioned embodiment 1, because of using the hard steel wire rod having 0.63 weight percents in carbon content, the processing quantity was increased in comparison with, for example, the wiredrawing in compared example 2 that was carried out to make the wire rod from the 4.5 mm wire diameter to the 1.20 mm wire diameter. However, because the carbon content was low and the material was soft, the wire rod after the wiredrawing was turned to pearlite structures in which ferrite and cementite were drawn in parallel with a narrow interval therebetween and with fine and smooth structures. Therefore, it became possible to easily obtain a wire rod of a desired wire diameter through one wiredrawing process without bringing about the breaking of wire and the breaking of wire at welded portions during the wiredrawing, and the tensile strength (2000 N/mm²) was also equal to that in compared example 2 and became as designed.

In carrying out breaking tests at welded portions of the material wires, eleven (11) material wires each being approximately 1 meter long were prepared for each of embodiment 1 and compared examples 1 and 2 and were joined by welding to make one wire by being repetitively subjected to welding, annealing and deburring in accordance with the welding procedure in each of embodiment 1 and compared examples 1 and 2. Thereafter, the wires each welded at 10 portions were wiredrawn to 1.20 mm diameter in a conventional method, and the number of breakings of wire was counted. The results were as described above (in Table 1).

Photos in FIG. 3 show in an enlarged scale the surfaces of the bead wires in the state that plated layers were removed from the surfaces of the bead wires each produced as shown in FIG. 2. In the bead wire, the anchor effect of its adhesion to rubber is influenced by groove intervals of wrinkles (unevenness) which are generated with an increase in surface area resulting from a decrease in diameter brought about by the wiredrawing. In FIG. 3, (A) shows the surface of the bead wire produced in the aforementioned embodiment 1, (B) shows the surface of the bead wire produced in the aforementioned compared example 1, and (C) shows the surface of the bead wire produced in the aforementioned compared example 2. Adhesion tests before and after the aging were carried out on these bead wires. Embodiment 1 had results that were better than those of compared examples 1 and 2 in both of an initial adhesion property before the aging and a waterproof adhesion property representing tyres that had traveled after the aging. On the other hand, in particular, compared example 2 had an inferior result in the waterproof adhesion property. From this, it was backed up that those in embodiment 1 and compared example 1 had the groove intervals being excellent in anchor effect in comparison with that in compared example 2.

The tests for adhesive forces were carried out based on the rubber adhesion testing method prescribed in JIS G3510. Embedded rubber of a conventional composition noted below was used as bead insulation. The numerals show ratios in mass. The ratios are natural rubber 50, SBR 50, carbon black 100 (SEAST® SO, manufactured by TOKAI CARBON CO., LTD.), softening agent 25, calcium carbonate 25, talc 10, stearic acid 2, zinc oxide 5, sulfur 8, and vulcanization accelerator 1.

The tests were done with an embedded length of each bead wire in the rubber set to 50 mm and a drawing velocity set to 150 mm/min, and visual evaluations were made regarding the drawing force, i.e., an adhesion force (N)—rubber adhesion rate (%) remaining on the bead wire. Those each with a plated layer of Cu/Sn=93/7 on the surface were used as the bead wires.

The vulcanization condition for the initial adhesion properties was for 40 minutes at 150° C., and the waterproof adhesion properties were evaluated by the aforementioned drawing adhesion tests after leaving the vulcanized samples in an atmosphere of 70° C. and 95% RH for one week. A condition in which tyres deteriorate due to heat after traveling was assumed for the waterproof adhesion properties.

The foregoing embodiment has been described taking the example that the hard steel wire rod of 5.5 mm in wire diameter having the chemical components of C: 0.63%, Si: 0.21%, Mn: 0.52%, and the remainder containing Fe and inevitable impurities was reduced in area through one wiredrawing process to the 1.20 mm wire diameter with the true strain in the range of 2.0˜4.0. And, almost the same effects as the forgoing embodiment 1 can be obtained in the case that a hard steel wire rod of 6.5 mm in wire diameter having the chemical components of C: 0.63%, Si: 0.21%, Mn: 0.52%, and the remainder containing Fe and inevitable impurities is reduced in area through one wiredrawing process to 1.55 mm wire diameter.

According to the bead wire in the foregoing implementation form, the carbon steel wire rod containing carbon in the range of 0.61% or more to 0.65% or less in weight percent and having the diameter in the range of 5.5mm to 6.5 mm is wiredrawn through one wiredrawing process to the predetermined final wiredrawing diameter with the true strain in the range of 2.0˜4.0, so that the wire rod is turned to pearlite structures in which ferrite and cementite have been drawn in parallel with a narrow interval therebetween. Therefore, although the carbon steel wire of the diameter for general purpose is used, it is possible to obtain a useful tyre bead wire which is superior in tensile strength, is excellent in adhesion force of the bead wire to surrounding rubber, and does not bring about the breaking of wire during the wiredrawing and the breaking of wire at welded portions. In particular, as a result of wiredrawing the carbon steel of the low carbon content at the high area-reduction rate, it is possible to realize the bead wire of the pearlite structures in which ferrite (Fe) and cementite (Fe₃C) are drawn in parallel with the narrow interval therebetween and with the structures being fine and smooth.

Further, according to the bead wire production process in the foregoing implementation form, since the carbon steel wire rod containing carbon in the range of 0.61 or more to 0.65 or less in weight percent and having the diameter in the range of 5.5 mm to 6.5 mm is wiredrawn through one process to the predetermined final wiredrawing diameter with the true stress in the range of 2.0-4.0, it can be realized to wiredraw the carbon steel wire rod of the relatively low carbon content at the high area-reduction rate without a patenting treatment. Thus, it can be done to wiredraw the carbon steel wire rod of the general-purpose wire diameter (5.5-6.5 mm diameter) through one process to the final wiredrawing diameter suitable for bead wire without bringing about the breaking of wire but with the required tensile strength secured.

Although the present invention has been described based on the implementation form, the present invention is not limited to the construction described in the implementation form and may take various forms without departing from the gist of the present invention described in the scope of the patent claims.

INDUSTRIAL APPLICABILITY

The tyre bead wire and the production process therefor according to the present invention are suitable to obtain bead wires used in producing bead cores which are reinforcement of automotive tyres.

DESCRIPTION OF SYMBOLS

11 . . . descaling treatment, 12 . . . coating fluid adhesion treatment, 13 . . . wiredrawing process, 21 . . . bluing treatment, 22 . . . plating treatment. 

1-5. (canceled)
 6. A tire bead wire, comprising: carbon in a range of 0.61% or more to 0.65% or less in weight percent; and a pearlite structure comprising ferrite and cementite, wherein the bead wire has a final diameter, wherein the bead wire has a true strain in a range of 2.0 to 4.0, wherein the ferrite and cementite have a narrow interval therebetween.
 7. The bead wire of claim 6, wherein the bead wire has a final diameter in a range of 0.94 to 2.20 mm.
 8. The bead wire of claim 6, wherein the bead wire has a final diameter in a range of 0.94 to 1.30 mm.
 9. The bead wire of claim 6, wherein the bead wire has a final diameter in a range of 1.5 to 2.20 mm.
 10. The bead wire of claim 6, further comprising Si.
 11. The bead wire of claim 6, further comprising Mn.
 12. The bead wire of claim 6, further comprising Si and Mn.
 13. The bead wire of claim 6, wherein the bead wire comprises carbon in a range of 0.61% or more to 0.63% or less in weight percent.
 14. The bead wire of claim 6, wherein the bead wire comprises carbon in a range of 0.63% or more to 0.65% or less in weight percent.
 15. A process for producing a tire bead wire, the process comprising: (a) wiredrawing, only once, a carbon steel wire rod comprising carbon in a range of 0.61% or more to 0.65% or less in weight percent and having an initial diameter in a range of 5.5 mm to 6.5 mm, to obtain a tire bead wire having a final diameter less than the initial diameter and a true strain in a range of 2.0 to 4.0; then (b) bluing the tire bead wire; and, after the bluing, (c) plating the tire bead wire.
 16. The process of claim 15, wherein, after the wiredrawing (a), the bead wire has a final diameter in a range of 0.94 to 2.20 mm.
 17. The process of claim 15, wherein the carbon steel wire rod has an initial diameter of 5.5 mm and, after the wiredrawing (a), the bead wire has a final diameter in a range of 0.94 to 1.30 mm.
 18. The process of claim 15, wherein the carbon steel wire rod has an initial diameter of 6.5 mm and, after the wiredrawing (a), the bead wire has a final diameter in a range of 1.5 to 2.20 mm.
 19. The process of claim 15, wherein the carbon steel wire rod further comprises Si.
 20. The process of claim 15, wherein the carbon steel wire rod further comprises Mn.
 21. The process of claim 15, wherein the carbon steel wire rod further comprises Si and Mn.
 22. The process of claim 15, wherein the carbon steel wire rod comprises carbon in a range of 0.61% or more to 0.63% or less in weight percent.
 23. The process of claim 15, wherein the carbon steel wire rod comprises carbon in a range of 0.63% or more to 0.65% or less in weight percent.
 24. A tire bead wire obtained by the process of claim
 15. 